Sulphonylated aromatic compounds are useful intermediates in a wide range of fields such as in agrochemicals and polymers (see for example U.S. Pat. No. 4,780,127). European Patent Application No. 455332 describes certain reactions of aromatic compounds in the presence of zeolite catalysts.
The normal reaction between an aromatic compound and alkyl sulphonyl halide in the presence of an aluminum trichloride catalyst gives approximately 50% para selectivity. The applicants have provided a process whereby the para selectivity of such a reaction is enhanced.